Electrical power distribution grids use electrical devices, such as transformers, capacitors and reactors to control the power on the network. Dangerous conditions can be created in such electrical devices when aging or operating stresses cause the insulation system to fail. A short circuit within such an electrical device can release a large amount of energy within a fraction of a second. In the worst case, the electrical device can explode due to rapid pressure surges from the vaporizing of the insulating oil and the decomposition of the oil vapor into combustible gases. Some electrical devices are filled with electrically insulating gases such as sulfur hexafluoride. In such gas-filled devices arcing can cause pressure surges in the gas.
Unfortunately, an internal fault within an electrical device may occur without providing a visible sign to the outside. Unless service personnel can tell that a particular device has failed, they may re-apply power to the device without detecting that a failure has occurred, exposing them to the significant risk that the electrical device could explode when reenergized and the fault reoccurs and generates a high internal pressure.